Indicating pin fuses include a biased pin that moves in a direction longitudinally thereof in response to blowing of a fuse to indicate that the fuse has blown. Striker pin fuses include also a pin that moves in response to blowing of a fuse, but the object of a striker pin is to perform some mechanical work in response to blowing of a fuse, e.g. to unlatch the latch mechanism of a circuit breaker. Both indicating and striker pin fuses may have identical design features, except that striker pin fuses must generally have a stronger biasing force, e.g. a stronger spring, since their striker pin is supposed to perform work, while an indicating pin is not supposed to perform work.
Indicating and striker pin fuses include an elongated means, such as a pin, that is responsive to blowing of the fuse. Normally the indicating or striker pin is restrained, or held captive, by the restraining wire or fusible element of the fuse. The fusible element is normally embedded in a pulverulent arc-quenching filler and the point where initial fusion of the fusible element occurs is normally unknown, i.e. its location is unpredictable. As long as the fusible element is straight, or V-shaped, the fact is of no consequence that the point of initial break formation is unknown because under such conditions the force biasing the indicating or striker pin is sufficiently high to move an interrupted fusible element inside of a body of pulverulent arc-quenching filler. This is no longer possible where the fusible element exerts a high resistance against the drawing force, i.e. the force tending to displace it, e.g. where the fusible element is wound helically. It is, therefore, the principal object of the present invention to provide electric indicating and striker pin fuses that operate properly though their fusible element is precluded, e.g. by friction, from sliding inside the pulverulent arc-quenching filler. Another object of the invention is to adapt conventional indicating and striker pin fuses, such as disclosed, for instance, in U.S. Pat. No. 3,697,916; 10/10/72 to Richard A. Belcher et al for ELECTRIC LOW-VOLTAGE FUSE for application in fuses whose fusible element that controls the operation of the indicating or striker pin is wound helically, or precluded for other reasons from moving inside the pulverulent arc-quenching filler into which it is embedded.
The closest prior art known to me dealing with similar problems are U.S. Pat. No. 3,832,665; 08/27/74 to Richard A. Belcher for BLOWN FUSE INDICATOR FOR HIGH-VOLTAGE FUSES, and U.S. Pat. No. 4,001,749; 01/04/77 to Frederick J. Kozacka for ELECTRIC FUSE FOR ELEVATED CIRCUIT VOLTAGES.